Conventionally, urethane compounds such as alkyl carbamates are useful organic compounds as industrial raw materials having a wide variety of applications such as a raw material for medicine and agricultural chemicals, a raw material for various fine chemicals, and a reagent for analysis of alcohols.
In recent years, various studies have been made to use such alkyl carbamate as a raw material for phosgene-free production of isocyanates.
Specifically, isocyanates are organic compounds containing isocyanate groups, widely used as raw materials of polyurethane, and industrially produced by a reaction between amine and phosgene (phosgene method).
The phosgene is, however, highly toxic and corrosive, resulting in inconvenient handling. Therefore, as an alternative to the phosgene method, an economical method for producing isocyanates has been recently proposed that produces an isocyanate by allowing amine, urea or carbamate, and alcohol to react to produce urethane compounds, and thereafter thermally decomposing the urethane compounds thus produced.
As the method for producing urethane compounds, it has been proposed, for example, a method for producing 2,4-di-(ethoxycarbonylamino)-toluol by allowing 2,4-diaminotoluol, carbamic acid ethyl ester, and ethanol to react in the presence of iron(II) acetate which is a Lewis acid catalyst made of a metal atom cation and a coordinating anion (see, for example, the following Patent Document 1, Examples 36).
Further, it has been proposed, for example, a method for producing 2,4-bis-(n-hexoxycarbonyl-amino)-toluene by allowing diaminotoluene, urea, and n-hexanol to react in the presence of zinc octoate which is a Lewis acid catalyst made of a metal atom cation and a coordinating anion (see, for example, the following Patent Document 2, Example 11).    Patent Document 1: Japanese Unexamined Patent Publication No. 55-149241    Patent Document 2: Japanese Unexamined Patent Publication No. 57-114561